Crohn's disease: prevalence, MR features, and clinical significance of enteric and colonic sinus tracts.

OBJECTIVES Enteric and colonic sinus tracts are inflammatory complications that precede intestinal fistulas in patients with Crohn's disease (CD). The aim of this study was to retrospectively determine the prevalence, morphologic features, and outcome of sinus tracts using MR imaging. METHODS A consecutive cohort of 642 patients with known CD, referred for MR enterography or MR enteroclysis (study period 01/2014-09/2019), was evaluated retrospectively for the presence of sinus tracts, their locations, presence and length of coexisting strictures, bowel wall thickness, CDMI score, upstream dilation, and bowel distension. Clinical outcome was assessed using medical records. For metric data, means and standard deviation, as well as one-way ANOVA and Pearson's correlation coefficient, were calculated. RESULTS In 36/642 patients with CD undergoing MRE, 49 sinus tracts (forty in small intestine, nine in left-sided colon) were detected with a prevalence of 6.9% in patients with MR-visible signs of CD (n = 519, overall prevalence of 5.6%). Mean segmental bowel wall thickness was 8.9 mm, and mean CDMI score was 9.3. All sinus tracts were located within a stenotic segment, showing mesenteric orientation within the small bowel and upstream dilation in 13 patients. Of 36 patients, 19 underwent immediate surgery and seven developed clinical progression within the segment containing the sinus tract. CONCLUSIONS Sinus tracts occur in 6.9% of patients with visible signs of CD. They are located within stenotic, severely thickened bowel segments with high MR inflammation scores. Their detection is clinically important, because they indicate a more aggressive phenotype and, if left untreated, may show severe progression. KEY POINTS • Sinus tracts occur in 6.9% of patients with MR-visible signs of Crohn's disease. • Sinus tracts are a radiological indicator of early penetrating Crohn's disease, with a high risk of progression, and require dedicated treatment. • Sinus tracts can be recognized by characteristic findings and typically occur in stenotic, severely thickened bowel segments with high MR inflammation scores.